Best use I'd say is to measure your resting heart rate in the morning before getting up from bed. Heart rate is a bit tricky, since there are so many things that influences it (how tired you are, temperature, food intake, hydration level), so it's hard to pin point exactly what the number you see on the HR monitor actually means.

Yup - I do this (kind of). I remember even from when I was a kid, recovery speed was a key sign of fitness - although there were less gadgets back in them days.

Resting HR is interesting - but that should be your total lowest (60 is normal, but I bet you can get lower if you are totally rested, lying down etc. I'm usually 42). But the range and speed of recovery depends on what you're doing. A really hard interval run might take me to towards 93% WHR (working heart rate which is [max heart rate - resting heart rate]) and then get back to 60% WHR in 90 seconds.

It's all quite relative, but if you build up stats it can show you improvements. Like Fredrik says there can be a lot of influencing factors - but I judge my general fitness by HR during a run / bike session (or perceived effort if you are gadget less) rather than speed.

I will have to play around with this and see how it can be applied to strength training. Interestingly my heart rate is higher when I wake up in the morning in bed 70bpm than when I am chilling on the couch in the evening 60bpm.Maybe just take my heart rate before each session and see if there is any correlation between a good a rubbish session.

I would think the best use for strength training is if you use it every time to get reliable data for what heart rate you usually have. If you then get anomalies you can suspect something like a cold coming up or you are about to get over trained.

Or having your HR right after a set and then watching how much time takes coming back to normal or how many bpms you drop after 60 seconds of rest. Then you could wonder in what circumstances your recovery is better and how much affect to the next set, or the whole day.

There's a table intented for runners, it's basically about measuring your hear rate right after running and then 60 seconds later to determine if you were pushing too hard or you're on the right pace depending on how many bpms you've lost.